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Example 17: In DABC, AC = 8 cm, BC = 4 cm, and AD = 5 cm. Find: A

(a) the area of the DABC 8 cm
(b) the length of side BE 5 cm E
Solution: In the given DABC, base of the triangle, BC = 4 cm,

height of the triangle, AD = 5 cm D B 4 cm C
We have,

1
(a) Area of the DABC = × base × height
2
1
= × BC × AD
2
1
= × 4 cm × 5 cm = 10 cm 2
2
1
(b) Also, area of the DABC = × AC × BE Think and Answer
2 What will be the area of a triangle
1
Therefore, 10 cm = × 8 cm × BE when the base is doubled and the
2
2 height remains the same?
10 5
BE = cm = cm = 2.5 cm
4 2
Thus, BE = 2.5 cm

Practice Time 13B

1. Complete the given table.

Base (b) Height (h) Area of a Parallelogram
(a) 8 cm 6 cm

(b) 12 cm 36 sq. cm
(c) 5.4 cm 34.56 cm 2
(d) 15.6 m 32.76 sq. m

2. Complete the given table.

Base (b) Height (h) Area of a Triangle
(a) 18 cm 154 sq. cm

(b) 22 cm 170.5 sq. cm
(c) 5 cm 3.2 cm

3. Find the area for the following parallelograms.
(a) (b) (c) (d)

4 cm 3 cm 3.5 cm 5 cm

7 cm 5 cm 4.8 cm
2.5 cm

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